A 53 year old, afebrile woman presented to the dermatology clinic with a two week history of petechial rash on her lower extremities that had progressed up to her arms. In addition, she also had pain in the wrists, knees, and elbows. Approximately five months earlier, she had been diagnosed with group A streptococcal pharyngeal infection, but she had not been treated with antibiotics. She was currently taking salbutamol, famciclovir, levothyroxine, lovastatin, and varenicline. A systems review was unremarkable and she had no reported haematuria, abdominal pain, or bloody stools.

A physical examination found multiple petechial macules, papules, and purpuric plaques, which were more numerous on the legs than on the arms (figure[F1]). A complete blood count and coagulation studies were normal. Urinalysis showed haematuria and proteinuria. A skin biopsy of a petechial papule revealed leucocytoclastic vasculitis, with a granular IgA reactivity around the blood vessels in the papillary dermis.

Questions

1 What additional investigative studies could be useful in a patient with palpable purpura?